One foggy Sunday morning, when most people were burrowing deeper under their bedcovers, 20 men and women stripped down to their swimsuits on the Pacific Palisades beach and waded into the 63-degree water.

After negotiating a strong surf, they swam toward a buoy in the middle of the bay until all that was visible was a line of arms plying through the gray swells.

The first 200 yards of the two-mile swim were cold and miserable, they said, until their heart rates increased. Then euphoria set in, until, toward the end of the swim, their bodies lost heat. At that point, many of the swimmers said they resorted to mind control to beat the cold as well as fears of sharks or other sea creatures.

In 45 minutes, the swimmers emerged shivering but safe. They met afterward on the deck at Gladstone's 4 Fish restaurant to swap stories and feast on sweet rolls, bagels and coffee.

The Malibu Polar Bear and Breakfast Club was in session.

The informal group, whose membership ranges from 6 to 25--depending on the weather--is dedicated to year-round ocean swimming. For the past two years, the swimmers have met faithfully at the beach every Sunday morning. The group includes two Olympic medalists, the record holder in a race from Alcatraz to San Francisco and the top two finishers in a swimming race around Manhattan.

It is not surprising that such a group would form on the Westside, said Richard Marks, who took second place in the 1983 Manhattan race and was the 18th man to swim the Santa Catalina Channel. "The Santa Monica Freeway puts you on the beach and that's it," he said. " . . . The last area to explore is the ocean. The ocean is very freeing. A pool, to a distance swimmer, is warm and confining."

Some members said they brave the ocean for the exercise and the camaraderie of the group. Others are trying to conquer a fear of sharks. And some said ocean swimming is a spiritual experience.

"Your week can be the most mundane in the world, but Sunday morning, as though we are going to church, we meet our group of ocean swimmers," Marks, a lawyer, said. "We do the service. No matter what the weather, we swim out to the buoy and come back to chat. We engage in something that is physical to the point of being spiritual."

Joe Prata, 57, a former high school swimming coach, said he swims in the ocean almost every day. "There's something so beautiful and clear and calm," he said. "It's like flying."

The founding of the group is unclear. Some say it was started by six swimmers who completed a relay from Santa Catalina Island to the mainland in 1981. Whatever the circumstances, its formation coincided with the increasing popularity of ocean swimming. Hundreds of participants flock to organized "rough water" races off the beaches at Pacific Palisades, Santa Monica, Malibu and Ventura, and the La Jolla Rough Water race draws up to 2,000 annually.

Most Malibu Polar Bear members previously competed in pools but said swimming in the ocean provides an entirely different sensation. "You feel a lot closer to your environment," said Peter Rocca, winner of two silver medals in the backstroke in the 1976 Olympics. "It's so relaxing. It touches a different part of you. . . . At first, I hated not following a black line."

(Sandra Neilson, who won three gold medals in the 1972 Olympics, also belongs to the group, members said.)

Thinks of Music

Mike Suttle, a free-lance trumpet player, said he thinks of music when he swims. It takes his mind off the cold water.

The cold plagues many of the swimmers who shivered as they clutched plastic cups filled with coffee and swapped stories on the deck at Gladstone's.

A major concern oof all of them is hypothermia, the loss of body heat that can lead to numbness and disorientation. Some wear two swimming caps, swim suits and wet suits to retain the body heat. But the swimmers said the most potent weapon against hypothermia is the mind.

"I used to hate the cold," Marks said. "Then I got to taking the cold along for the swim. I will say, 'This is beautiful; this is great and exhilarating. . . . And it's also cold.' "

Susan Deitz, a secretary, recalled a swim in which she became disoriented. Rather than return to shore, she decided to "swim through it," she said, and make it a case of mind over matter. "If you are running a marathon, you can stop and sit down. But if you are swimming, it's a mental discipline." Members warned against swimming alone, citing the danger of cramps, becoming lost in the fog or swallowing salt water. Novices should swim with more experienced swimmers, they said.

The uncertainty of ocean swimming attracts many to the sport. "A lot of pool swimmers want to know the conditions," said Harald Johnson, editorial director of Triathlon Magazine, who won the swim around Manhattan in 1983. "They want everything to be secure. Rough-water swimmers don't know what's out there. There are sharks out there."